Nov. i, 1920 Effect of Drying Disinfected Seed Wheat 2 1 9 



To detect the presence of formaldeyde on treated seed, Tollen's "sil- 

 ver mirror" aldehyde test 1 was used. To obtain comparable watei 

 extracts of the seed lots a uniform procedure was adopted which con- 

 sisted in extracting 15 cc. of the wheat sample with 10 cc. of distilled 

 water for two minutes in a 100-cc. graduated cylinder which was ro- 

 tated and shaken constantly to wash all the seeds as thoroughly as pos- 

 sible. Five cc. of the washings were then transferred to a test tube by 

 means of a pipette. Extracts of all the wheat samples to be studied 

 were thus prepared before proceeding. This is because it was necessary 

 to add the reagent to all at as nearly the same instant as possible in 

 order that results given by color changes might be comparable, since it 

 is by the relative rapidity of their appearance that the relative quantities 

 of precipitate formed by the presence of formaldehyde are shown. One 

 cc. of Tollen's reagent was then added quickly to each tube by means of 

 a pipette, and the tubes were watched for the appearance of the black, 

 or, at first, dark brown precipitate indicating the presence of formal- 

 dehyde. The relative quantities of formaldehyde present in the tubes 

 were shown by the rapidity of formation and by the density of this 

 precipitate. 



Several interesting facts were disclosed by the application of this test 

 to the washings of treated seed. In the first place, distinct and positive 

 reactions were invariably obtained from seed which had been drying for 

 weeks, thus giving a clue to the reasons for the cumulative injury suffered 

 by seeds in drying. Positive reactions were given by extracts of samples, 

 the germinations of which were reported in Tables I and II, after the 

 seed had dried nine weeks in the laboratory. This, however, was longer 

 than thcaverage persistence of the paraformaldehyde, which, on account 

 of its volatility, usually disappeared in a month, depending on the con- 

 ditions of drying. It is understood, of course, that, in the presence of 

 moisture, paraformaldehyde at once breaks down and is again formal- 

 dehyde in solution. 



In addition to this proof of the persistence of formaldehyde on the 

 seed in the form of paraformaldehyde, the qualitative tests showed in- 

 variably that about 24 hours after treatment there was more formalde- 

 hyde on the seed stored damp in a sealed jar than on that treated at the 

 same time and stored dry, showing a diminution in the quantity as the 

 seed dried. After 48 to 72 hours, the amount on the seeds in the sealed 

 jars had diminished at a more rapid rate, so that extracts from them gave 

 weaker and slower reactions than those from the dried seed. Within a 



1 Tollen's reagent is an ammoniacal solution of silver nitrate which when added to a dilute aldehyde 

 solution produces a black precipitate or, upon standing and in the presence of a sufficient amount of the 

 aldehyde, forms a silver mirror by the precipitation of metallic silver on the sides of the test tube or other 

 container. It is made by dissolving 3 gm. of silver nitrate in 30 gm. of water and 3 gm. of sodium hydroxid 

 in 30 gm. of water, the two solutions being kept separate until ready for use, when they are mixed in equal 

 parts by volume and the resulting precipitate of silver oxid is dissolved by the addition, drop by drop, of 

 ammonia (specific gravity 0.923). 



